In a healthy heart which is composed of four chambers, atria collect the blood from body and the lungs, and the ventricles pump the blood to the lungs and the body. The oxygenated blood which is pumped by the left ventricles carries oxygen to the body. Deoxygenated blood is returned to the right heart via veins and pumped to the lungs via pulmonary artery originated from the right heart. The oxygenated blood in the lungs flows into the left atrium via pulmonary veins and then to the left ventricle where it is pumped to the body. Right and left chambers of the heart are separated by a wall to avoid the mixture of oxygenated and deoxygenated blood. Congenital opening between right and left atria of the heart is called as ASD (atrial septal defect). In the presence of an ASD, oxygenated blood in the left atrium flows into the right atrium, and the amount of the blood to be pumped by the right atria increases. In time, this would lead to overload, hypertension in the pulmonary arteries (pulmonary hypertension) and heart failure, decreasing life expectancy. Moreover, the emboli passing through this hole may reach to the brain leading to strokes. If the blood flowing through the left atrium to the right atrium is above a certain amount, ASD must be occluded. Otherwise, irreversible damage may occur in the pulmonary arteries.
In the fetal heart, there is a hole (foramen ovale) between the atria, and this hole is partially covered by a membrane. This hole between the membrane allows the blood to pass from right to left atria, and it is vital for the baby. Following the birth, the membrane closes the hole, and in few months the hole is completely occluded in most cases.
The Atrial Flow Regulator (AFR) or the blood flow regulating device, as referred to as below, is intended to create a hole (small ASD) between the two collecting chambers in the heart (right and Left Atria), i.e. opposite to the purpose of an occluder. This will allow flow of blood from a chamber that is stiff and under high pressure to a chamber that is less stiff and under lesser pressure. By creating such a hole, symptoms resulting from back flow of blood into the areas filling that chamber could be prevented. For example, if the pressure in the left atria (LA) is high then the back pressure would be into the lungs from which the oxygenated blood is draining into the LA. This causes the patient to be breathless and give symptoms like coughing and an inability to lie flat or climb stairs. Creating a hole in the atrial septum will decompress the LA into a less-stiff and low pressure Right Atrium (RA). This would help the patient to be free of such symptoms. Similarly, if the Right Atrium (RA) is under high pressure or becomes stiff from a failing Right Ventricle (RV), the chamber can be decompressed by a hole created in the atrial septum. This will reduce symptoms from high pressure in the veins draining into the RA like liver veins, kidney veins, veins from the intestine, etc.
When such a hole is created, it should be calibrated so as to control the amount of pressure drop and amount of blood flowing through the hole. When blood flows from the RA to LA, the patients may become bluer but will have better blood flow into the vital organs. If the blood flow is from LA to the RA then there is no problem with saturations but there may be a slight reduction in blood flow into the organs during more than moderate exercise which otherwise would have been not possible in those patients.
Although rare, there are some risks during the transcatheter procedure. While attempting to make a hole to implant the AFR, laceration or bleeding may occur in vessels which may require surgical invention or blood transfusion. Infection is another risk following the procedure, which may require antibiotic treatment. Very rarely stroke and accordingly long term function loss may occur. Allergic reactions or loss of renal functions may develop due to contrast material. Creating a hole may also predispose the patient to paradoxic embolism and stroke if the blood flows from right to left.
Urgent surgical intervention may be needed due to inappropriate location of the AFR device or premature release of the device form the catheter. The device can be dislocated after being released and it may harm the adjacent heart valves. This situation may require operation. Rarely, the device may not be implantable or clots can form around the device, leading to embolism.
Sivaprakasam M, Kiesewetter C, Veldtman G R, Salmon A P, Vettukattil J. published an article “New technique for fenestration of the interatrial septum” j intery cardiol In 2006 Aug. 19(4):334-6. This was created by improvised use of a stent not intended for this use. However, it is important to ensure that the defect created in the heart is a precise diameter to a calibrated size to allow appropriate amount of blood flow, just enough to maintain the necessary cardiac output without causing other complications like severe decrease in oxygenation, device dislodgement, decrease in the size of hole in the device etc. It is equally important that such devices are precisely positioned to avoid damage or dysfunction of healthy heart tissues or structures.
Prior devices for creating a shunt or an opening in the heart have a middle section, which can be called the conjoined ring, which is circular and provides most of the support to the right and left disc-shaped end sections in order to keep its circular shape and calibrated diameter, and to keep its shape memory. Such a device can be placed between two cardiac chambers. To allow pressure reduction between the two cardiac chambers, a manual hole is made by splaying the wires of the device. A problem with previous devices is lack of stability and thereby difficulties in attaining a well-defined calibrated opening. Moreover, with conventional devices, due to the hole being in the ring that latches on to the wall or septum (partition between the two chambers), the hole may get covered in the process of endothelialisation, i.e. the natural process of the body to cover any foreign material. A further problem with prior art device is the disruption of the endothelialization process, which can cause formation of embolies travelling in the blood stream.
Thus with prior art device there is a challenge to achieve sufficient stability, a sufficiently well-defined shunt, and reduced risk of formation of embolies.
Thus, it would be advantageous to provide an improved blood flow regulating device with improved stability, allowing for improved support, and the ability to retain the calibrated size, and improved properties with respect to endothelialization, as well as a method of manufacturing such device.